Electric lamp



L. THORINGTON Jan. 5, 1960 ELECTRIC LAMP Filed Aug. is. 1957 5 Sheets-Sheet 1 P r l A TL.

(mf/0 'wv 90200) wwf/7H lo #v9/MLM! /v/ DA1 INVENTOR.

wf/5 //o/e/A/ra/v 15 LQQJ 47m/ways Jan. 5, 1960 3 Sheets-Sheet 3 Filed Aug. 15. 1957 f1 u M s w R; LMO@ @Z WMQU M 0. 7 0 mm Mi E M@ Y B 4 Z mM www y x 5m M 0 732 o a Z Z CM: K n. M J a w w m .iw WM m M www H m am MT wm /Zo ZZ Gm# n 2]/ WMM w mfrm M @NF a f5. wm f n M R W P 0E mi M P 06 n M m w m l ELECTRIC LAMP Luke Thorington, Berkeley Heights, NJ., as signor to Duro Test Corporation,North Bergen, NJ., a corporation of New York Application August 13, 1957, SerialN'o. 678,013 8 Claims. (Cl. 313-109) This invention comprises a new source of light which generally speaking is an incandescent lamp producing light composed in part of the visible energy produced by an incandescent filament and the remainder from .-the illumination of active gas excitation of phospho'rs." The nature of importance of the light sourcewhereinY rdisclosed will stand out best against the following ,gen- .eral background of lighting facts.

All artiiicial electric illuminants in use today fall into the classilication consisting of incandescent, gas diszcharge, iluorescent, electroluminescent, and combinations of one or more of the above.Y Except for electrolumi- Enescent sources which as a practical matter are only of .interest as a novelty, al1'these sources are widely used commercially throughout the world. As is of course vWell understood, of all these sources incandescent lamps .are by far the most widely used. This results from the :fact that at the beginning this type of light source had no real competition.- To its advantage is the fact that it is extremely simple and requires no auxiliary devices in its operation. Furthermore, it yis cheap and can be 2,920,222 Patented Jan. 5, 1960 2. lamp is Ygreatly increased by raising .the temperature of the filament, as can be established by well known laws, but of course, as a result the useful life of the lamp is short. For example, the temperature of a 100 watt lamp filament is adjusted to about 2850 K. for a life of about 750 hours and an intial eiciency of 16.3 lumens per watt (l./W.). lf the temperature of the v'iilament is adjucted to approximately the melting point of tungsten (3643 K.) theoretically one would attain 52 l./w., but the life of the ilament will be only a fraction of a second. This example serves as a reminder of the interdependence of lament temperature and life of an incandescent lamp. j As is well know in the art, this method of increasing lampeiciency has been greatly studied and as a result at the present time incandescent lamps are adjusted to operate at the optimum light eliicien'cyl for design life and no further improvement in this respect Ycan. be anticipated.

lIt been been proposed to utilize the normally wasted ,infraV red energy by the use of a selective infra red V'reflector such as titanium dioxide coated on both sides of a spherical bulb in which a specially wound compact filament is accurately positionedat the center. This results inan increase of eiciency of about 11%. 'Ihis coatingfreflects the-,normally Y,Wasted infra red energybackl onto the filament while. visible radiation is allowedto-pa'ss ."tlirough'the coated-bulb wall. As a readily manufactured for operation over a wide range :of voltage. Finally, its color rendition of the human skin is flattering.

The incandescent lamp has attained and `continues to hold its outstanding position as a light source, surprisingly enough in spite of the fact that 90% of the input power is utterly wasted as far as useful illumination is concerned. It also has the important disadvantage that its color as distinguished from its color rendition' can be varied in only the narrow range of about 2500 to 3000 degrees K. (color temperature) at anywhere near acceptable eiiiciency.

Broadly speaking the invention hereinafter disclosed involves improvements in incandescent lamps whereby` these disadvantages are substantially overcome without sacrifice of any of its other advantages. A brief review of the present day incandescent lamp will be helpful in evaluating these improvements as will some 'considera-- tion of various other attempts and proposals made to date for improving incandescent lamp eliiciency and color.

0f the input power which may be considered as wasted from the operation of an incandescent lamp, the following classification indicates its components:

` The production of visible radiation by an incandescent standard present day commercial product vwill be much result of this type of operation less input Ypower is required to 'maintain the lilament at a given temperature of operation; The cost of making such a lamp, however, appears to be prohibitive when related to the relatively small gain in lighting eiliciency that is attained.

' The power loss due to conduction and convection of heat from the filament -by the fill-gas is related directly to the thermal conductivity of the gases within the bulb. At the present time the most common till-gas for incandescent lamps consists of various mixtures of nitrogen and argon. As is well understood by those skilled in the art the thermal conductivity of the-following gases decreases in the order listed, viz. H2, N2, Ne, Ar, Kr, Xe. Unfortunately the rareness of these gases increases in the same order. If krypton were lused in place of argon the eiciency of. an incandescent lamp would increase by about 20%. However, even with a gain 'as great as this the cost of substituting krypton for argon is prohibitive at the present time. A slight gain in eiiiciency can also be attained by increasing the ll-gas pressurein spite of the fact that the power loss due to the presence of the gas would also be increased. This results from the fact that the filament temperature can be increased slightly at higher gas pressures without increasing the rate of tungsten evaporation. A reduction in the overall surface area of the filament also reduces the gas loss which is why the industry has gone to coiling, double c'oiling and the like, but this source of improvement has apparently been exploited to the fullest in present day commercial incandescent lamps.

Losses vofpower due to absorption by the bulb andv Vbut the results attained are not of major importance.

Thus it will be seen from the above general description that even disregarding cost and followingy known procedures it cannot be expected that the maximum improvement in the eiciency of incandescent lamps over the teristic.

(2) The thermionic emission.

(3) The near ultraviolet and blue radiation emission.

The first property is employed in a known combination discharge-incandmcent lamp in 'which the filament acts simultaneously as a current limiting device for the discharge and as a source of red-rich radiation. combination the discharge source usually supplies most of the illumination and it can hardly be proper to say, therefore, that this lamp is an improved incandescent lampi. However, it has certain useful properties desired by an improved incandescent lamp, as for example higher efficiency (up toabout l./w.), wider color variation and the ability to operate without auxiliary devices. Unfortunately, its cost is relatively high and it has the undesirable property of not starting immediately after power interruption.

Utilization of the normally wasted thermionic emission of a hot tungsten filament to excite cathodo-luminescence in a special bulb coating has been suggested. Unfortunately a successful lamp of this type awaits development of satisfactory coatings which are suficiently responsive to the very low accelerating voltages available, without transformation. In its simplest form this lamp is an ordinary incandescent lamp with a phosphor coating deposited over aY transparent electrically conducting coating onV the inner surface of the bulb. The conducting coating is connected electrically either to the midpoint of the fila-y ment or to one side of the line. In the latter case luminescence is obtained on alternate half cycles at full line voltage while in the former case luminescence oc:-v

curs on consecutive half cycles but at half line voltage. Although the theoretical eiciency of this lamp is fairly high (about 30-40 l./w.) so would be the cost involved in applying the additional coating and connections, the latter of which are diicult to mak Although only a relatively small amount of ultraviolet radiation is produced by an ordinary incandescent lamp it is still suicient to effect some improvement in.

efficiency if it is utilized by the proper phosphor coating. The gain for an ordinary 100 w. lamp with such a coatingI would be only about 3% but this is attained without changing the basic lamp design and hence without greatly increasing cost. If maximum efliciency gain without regard for color is a 20% improvement by utilizing all the radiation below about 5200A. and converting it into narrow band luminescence emission peaked at 5550 A. This would be a worthwhile improvement but that too awaits the development of a suitable phosphor powder. In addition from the standpoint of color such a light source would be undesirable for general illumination since it is totally deficient in blue and violet radiation.

An, ideal solution of this problem would be one involving a coating for transforming the infra red radiation into Visible radiation. This phenomenon has not heretofore been observed but its possibility on fundamental grounds is recognized. Broadly speaking it would amount to stepwise excitation of a phosphor by several infra red quanta with subsequent emission of a single higher energy (visible) quantum. It is through this approach that substantial efficient improvement in the ordinary tungsten lamp would be desirable, given the secret to effect it. Stated another way, an ideal source of improvement of the tungsten lamp as it is known commercially today would beto convert the heat into light by a process more elicient than simple incandescence of the tungsten. This solution has long been desired and it is disclosed below.

In thisl desired, it is possible to attainf Aboverthis temperature Wc for hydrogen may be as highA In accordance with this invention use is made of two phenomena, the first is the phenomenon of dissociation of hydrogen molecules into atoms in the presence of a hot tungsten wire which catalyzes this dissociation. The other is the phenomenon of excitation of certain phosphors by active (dissociated) gases. In accordance with this invention these two phenomena are utilized in a combination which is structurally simple and inexpensive to manufacture. This combination is basically that of the present day commercial incandescent lamp modilied to utilize these two phenomena to greatly improve the efficiency of an incandescent lamp.

With respect to the first phenomenon let us assume an incandescent lamp to be filled with hydrogen gas instead of nitrogen or argon or mixtures thereof. In order to maintain the normal operating temperature of the filament additional power would have to be supplied to the lamp because of the increased cooling effect due to the presence of hydrogen. The cooling effect of this fill-gas follows the generally relation, up to a temperature of about 1900 K.

WhereY Wc=power carried by ordinary heat conduction and convection S =shape factor and depends on the diameter of the l wire and the nature of the gas and K=coeflicient of heat conductivity of the gas.

astwenty times that predicted by Equation l while all other gases follow the relation quite closely.

A comparison `between Wc for nitrogen and hydrogen at a pressure of 50 mm. (Hg) and at varioustemperaturesis shown in Fig. l. Other gases such as argon, krypton, etc. which show a similar curve to that of nitrogen but slightly below the latter because of the lower thermal conductivity of these heavier gases.

v AtV this point it may be noted that in the accompanying drawings:

Figures l, 2, 3, 4 and 5 comprise charts showing the relationship between various indicated factors as coordinates as appears therein respectively;

Figure 6 is an elevational view of an incandescent lamp in accordance with this invention, showing the envelope in cross-section;

Figures 7 and 9 are elevational views showing the envelope in cross-section of other forms of lamp in accordance with this invention;

Figures 8 and 10 respectively are top plan views of the lamps of Figs. 7 and 9; and

Figure 1l is an elevational View of still another form of lamp in accordance with this invention showing the4 envelope in cross-section.

This peculiar behavior of hydrogen is due to the catalytic dissociation of hydrogen molecules into atoms by the hot tungstenrwire. The mathematical relation which describes the cooling effect of this particular gas is:

W =Wc+Wd (2) where W :total power carried by hydrogen gas Wc=power carried by ordinary conduction Wd=power carried by dissociation of hydrogen.

creases with decreasing pressurergcontrary towhat might be expected and which is true ofv nitrogen.- The answer to this startling increase is -foundin theq-fact that the degree of dissociation Vof`hydrogenincreases-With decreasing pressure so more and more powerjs carried by this means until the effect of actual reductionV of the number of hydrogen molecules present begins to outweight the increase in degree of dissociation.

In the light of these observations and other evidence which could be presented it can be deduced that hydrogen molecules are in fact dissociated into atoms by a hot tungsten filament. This is so in spite of the fact that the energy necessary to tear apart the molecule is very large, viz. about ,4.5 electron volts. This compares with the energy of the 2537 A. quantum (about e.v.) which is the predominant radiation from the low pressure mercury discharge which excites the phosphor coating in lluorescent lamps.

Once the molecule is dissociated the constituent atoms will remain free until collision with other similar atoms occurs, whereupon recombination takes place with subsequent release of the tremendous energy originally required to separate them. This distance, the mean free path, traveled by hydrogen atoms before collision is effectively increased by a factor of 4.2 over that for hydrogen molecules because of the apparent ability lof hydrogen atoms to displace a hydrogen atom from a hydrogen molecule with which the former has collided, thus liberating another atom of the latter. The effective mean free path of hydrogen atoms is about 5.5 cm. at a hydrogen pressure of 0.015 mm. (Hg) and about 0.168 cm. at a pressure of 4.4 mm.

Ordinarily energy released when hydrogen atoms react to form molecules is in the form of heat. A commercial example of the use of this phenomenon isindicated in the principle of operation of the atomic hydrogen torch. In this torch a stream of hydrogen gas is passed through 'a high voltage discharge between tungsten electrodes where it is decomposed into hydrogen atoms which subv sequently recombine on the surfaces to be heated releasing to it the energy of recombination as heat. As will be explained below the energy liberated upon recombination of hydrogen atoms can be converted into light.

Phosphors are best known in the lamp industry for their ability to recouvert ultraviolet radiation into light. Such materials can be excited in a number of other ways, as vfor example by electrons, ions, electric ield, X-rays, alpha particles, etc. In accordance with this invention and as has been observed as a separate phenomenon, certain materials are excited to produce Yvisible light in the hydrogen flame. For example, magnesium aluminate: Mn emits a brilliant green luminescence when a hydrogen arne is played over its surface. This luminescence occurs at the boundary between the flameand the atmosphere. Zinc oxide and zinc sulfide: Cu phosphors also exhibit the same phenomenon. This emission is not a momentary thermoluminescence which would require a preexcitation by ultraviolet or electrons but continues as long as the-ame is applied.

Luminescence is also excited in phosphors when they are exposed to active (dissociated) gases such as nitrogen and hydrogen. Many phosphors includingthe oxides of Be, Mg, Ca, Zn, Sr, Cd, Ba, and the sulfides of Cu, Zn, Sr, Ba, B, Al, Ga and Ce show the phenomenon.V These in some cases mayk contain Mn, Bi, Ag, and Y as activators. Zinc silicate: Mn and boron nitride: C also show the phenomenon as well as a number of organic phosphors. Of special interest are data showing the temperature dependence of luminescence for excitation by active nitrogen as compared with that for photoand cathodoexcitation. It is known that active hydrogen shows the same results but experimental diiculties are greater than with active nitrogen. Curves for zinc silicate: Mn and boron nitride:C are reproduced in Figs.4 and 5. As a scienfluorescent tubes.

tiiic fact it is especially fortuitous that active gas excit=A tion is in general a high temperature phenomenon, since high temperature operation is `an inherentY property of the incandescent lamp.

' There will now be described the manner -in which, in accordance with this invention,"the etliciency of an incandescent lamp may be greatly improved.Y An example ofthe lamp is illustrated somewhat diagrammatically in Fig. 6. Basically itis of l,the usual construction, comprising asealed glass envelope 10 of suitable conguration having a .re-entrant stem 12 on which is supported, in accordance with any suitable construction, a tungsten lament 14. Applied to the neck of the bulb is the usual base 16, `consisting of -a thread forming shell 18 and an insulated center contact 20. The shell and contact are respectively connected to the ends of the filament by the leads 22 andl 24. g

The bulb 10 is coated on its inner surface with a coating 26 of any single one or a mixture of two or more of the phosphors listed above, as showing the phenomenon discussed in connection therewith. They might, as there stated, contain an activator. For example, this coating may consist of zinc'. silicate: Mn. The coating can be applied in .any number of different ways suitable to the purpose, as for example by the methods which are now used for coating incandescent lamp bulbs and The thinness of the coating is not critical but obviously it is preferable that it be made as thin as possible, consistent with the objects of this invention in order tol make the coated wall an ecient the `manufacture of ordinaryincandescent lamps and` hydrogen is introduced at relatively low pressures as explained below, and the bulb sealed. Of course, other processes used in the manufacture of incandescent lamps to increase their light eiciency may-also be used.

From the above it will be seen that strickly speaking ythe changes required in a standard incandescent lamp to incorporate subject matter of this invention are relatively simple and inexpensive. Also, these changes do not alter the appearance in any substantial manner of the lamp nor change the conditions of its use.

For operation power is applied to the filament in the normal way to 4maintain it at thedesired operating temperature. Hydrogen molecules impinging on the hot lament are absorbed and'dis'sociated i'nto atoms and subsequently are emitted from the filament.v At suciently low pressures the atoms travel unimpeded until they strike the coating on the bulb Wall, whereupon they recombine on the surface Yof the coating to form molecules again with the release of energy to the coating. This coating converts this energy into visible light and the hydrogen 'molecules `thus formed desorb and eventually return to the hot tlament` to begin another cycle.

Assuming a filament temperature of 2500 K. it is possible to determine, as will be explained below, theoptimum hydrogen pressure of the gas-lill. If the lamp were operated at higher temperatures appreciably higher hydrogen pressures would be required to retard filament evaporation and this would result'in too high a value for Wc, the power conducted away by the gas. The relation at various pressures of gas between Watts/cm. radiated (WR), watts/cm. carried by the gas j (W=W+Wn) total watts/cm., watts/cm. due to dissociation of hydrogen (WD) lumens/cm. radiated, theoretical lumens/ cm. obtainable from WD, and finally eciency in lumens per watt, have been set forth in Table I.

7, TABLE I Wattagaylumen and efficiency relations for tungsten wire in various pressures of hydrogen gas Hz Press., Wn W Wiz-HV WD L f LD Lt L/W 42 2. 24V 4() 18. 2 4 58. 2 26. 0 l. 58 3. 40 1. 48 f 18. 2 148 166. 2 48. 9 4. 85 6. 67 4. 19 18. 2 419 437' 65. 5 8. 21 10. 03 7. 1 18. 2 710 728 72. 8 10.` 2 12. 1- 7. 8 19. 2 780 799 66. 1 14.75 16, 4 9. 9 19. 2 990 1009 6l. 5 19. 20. 9 12. 5 19. 2 l., 250 1, 269 60. 6 17. 8 19. 7 9. 4 19. 2 940 959 48. 6

WR=watts/cm. radiated by Wire.

W=watts/om. cooling by hydrogen (Wc-{- Wa) WB+W=watts/cm. total supplied to filament.

WD :watts/cm. to hydrogen dissociation.

L f =lumens/cm. radiated from filament at 2500J K.

L n =lumenslemtheoretically attainable from dissociation of hydrogen and recombination on optimumV green phosphor.

Lt=lumens/cn1. total.

L/W=lun1ens/watt efoiency (theoretical).

Wire diameter= .00706 cn1.=.00278 inch.

As noted in the table above tabulation is per centimeter of wire of diameter 2.78 mils. Theefhciency of the filament at 2500 K. has been taken to be l0 l./w. and the theoretical efficiency for conversion of WD to light is taken to be 100 l./W. The latter is a reasonably ac-v curate theoretical figure for a narrow band green lumi nescing phosphor peaking at 5550 A. Actually if one assumed 100% energy conversion eiciency of WD into a luminescence spectrum having a luminosity factor of 0.9, then a maximum luminous efficiency of about 600 l./w. would be obtained. This of course could never be attained because of quantum considerations.

fit is apparent from Table I that optimum lamp efiiciency will be obtained at a hydrogen gas-fill' pressure approximately 4.4 mm. (Hg). free path of hydrogen atoms in hydrogen is very small as seen from Table II.

The significance of this is that some of the hydrogen atoms would recombine to form molecules before reaching the coating and bulb wall and this, of course, would result in a corresponding loss in light efficiency. The best pressure for the hydrogen gas-fill is about 0.2 mm. where the filament-coating distance is of the order of 0.4 cm. and with this combination the light efficiency attainable is approximately 50 l./w.

Such a dimension suggests a lamp of cylindrical design with an axial filament as the best compromise, although as suggested above the subject matter of this invention will produce useful` results employing the usual incandescent lamp geometry.

With regard to the filament it is .best lthat it have as great a surface area as possible. In other words a straight filament. As a practical matter this is an interesting contrast with the tendency today in incandescent lamps of reducing the area of the filament by using single, double and triple coilsy forthe purpose of reducing the vgas loss. Thus. the, filament construction ,is'simplifie'd inthe combination of this invention.

At this pressure the mean A ported by Wire hooks in a manner known in the art.A

Itis important to note that the lamp of this inventin' does notrequire theV use of subtractive filters toobtainf variation in` color and color rendition of the source.

Colorv choice is assimple as in the case of fluorescent' lamps where by theselection ofthe proper coating from f the viewpoint of light emitted a wide range of resultantV light with respectv to color is attainable.

Another advantage of the lamp of this invention isfthat the light therefrom is inherently rich in red and deep red radiations, a color difiicult'to obtain with fluo-f resce'nt lamps.

The lamp of Figure 6, as described above, illustrateshow a useful light source in accordance with this invention can be made with substantially no changes in' the construction of the ordinary incandescent lamp. However, as is apparent from the foregoing description, thisf physical form of lamp is not as efficient a production of'l A..

the subject matter of this invention as is possible. more efficient form of lamp is one in which the tungsten filament to phosphor spacing is such that maximum bom? This spacing is' determined in part by the pressure of the hydrogen fillI That is the spacing may be greater'V It is alsov bardment by hydrogen atoms occurs.

for the envelope. the lower the pressure of the hydrogen fill. important that the temperature of the phosphor be maintained sufficiently high so that desorption of thehydrogen gas takes place readily. Naturally the temperature of the phosphor will in part be detenninedby its distance fromthe hot tungsten filament. This temperature maintenance is necessary otherwise a layer of hydrogen may build up on the phosphor surface and render it' inactive. As appears from the abo-ve, the temperature of"l the phosphor should correspond to the temperature of peak excitation by active gases, as for example the hydrogen, and of course Iwill vary, depending upon which phosphor or mixtures'thereof are used, as will be Well understood by those skilled in this art.

For these among other reasons a lamp having a cylindrical envelope provides a more eicient geometry thanv that `of the present standard incandescent lamp, as di With this arrangement the tungsten filament 14 extends back and forth between the hooks which are mounted in the tube 28 to physically distribute the filament on a substantially cylindrical path about the support 28, as is clear from Figure 8. By adjusting the dimensions of this structure it will be seen that the various legs of the filament 14 will extend more or less parallel to the phosphor coating 26 on theinner surface of the bulb 10` and can be properly spaced in accordance with theabove consideration. The light efiiciency of this lamp can further be increased byV applying to the outer surface of the tubular insulating support V28 a similar coating 26,5 of phosphor, as indicated in these figures.

Figures 9 and l0 diagrammatically illustrate still another form of lamp in accordance with this invention wherein the above mentioned factors are taken into ac` count. In this arrangement there is mounted on the stem tube 12 an insulating support 30 which, as illustrated in Figure l0, forms a series of semi-cylindrical chambers in whichk the various legs of the filament 14 are respectively mounted more or less at their centers. The semicircular walls of these cavities can also be coated with the phosphor coating 26, as diagrammatically illustrated, so as to be similar in this respect to the lamp of Figure 7. The parts `of this lamp of Figure 9 can be dimensioned vvto provide'fo'r Jthe most eihcientl spacinglof-th'e In this figure the samel coatings and hot tungsten iilament legs. These cylindrical forms of lamp are subject to geometrical design adjustments which make them more efficient for the purposes of this invention than the modified standard lamp of Figure 6.

There is diagrammatically illustrated in Figure 11 another lamp in accordance with this invention in which instead of using a phosphor coating a gas or vapor atmosphere is suggested and is mixed with the hydrogen atmosphere. This lamp operates in accordance with the basic principle described above, but the recombination of the hydrogen atoms takes place in contact with the gas or vapor mixed therewith to convert the energy of recombination into visible light. In this lamp phosphorus, for example, can be used in place of the phosphor coating. By way of clarifying the action of the phosphorus the following equations may be helpful:

Hot

(Vapor) These equations are not intended to convey the exact mechanism of the reaction of phosphorus and hydrogen atoms but only to indicate a possible explanation. AsV

is clear from these equations the phosphorus is not used up in this reaction but recycles so long as the tungsten filament operates at a sufficiently high temperature, as for example about 2500 K.

From the above description it will be apparent to those skilled in the art that the subject matter of his invenion is capable of taking various useful forms, and it is preferred, therefore, that this disclosure be taken in an exemplary sense and the scope of protection afforded be determined by the appended claims.

What is claimed is:

1. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source of radiant energy in said envelope, a gas or vapor in said envelope at or below a pressure of 200 millimeters which dissociates in the presence of hot tungsten, and another substance in said envelope which converts the heat of recombination of the dissociated gas or vapor into visible light. v

2. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source lof radiant energy in said envelope, hydrogen in said envelope at or below a pressure of 200 millimeters which dissociates in the presence of hot tungsten, and another substance in said envelope which converts the heat of recombination of the dissociated hydrogen into visible light.

3. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source of radiant energy in said envelope, a gas or vapor in said envelope at or below a pressure of 200 millimeters which dissociates in the presence of hot tungsten, and a phosphor in said envelope which converts the heat of recombination o' the dissociated gas or vapor into visible light.

4. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source of radiant energy in said envelope, hydrogen in said eu- Velope at or below a pressure of 200 millimeters i which dissociates in the presence of hot tungsten, and

a phosphor in said envelope which converts the heat of recombination of the dissociated gas or vapor into visible light.

5. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source of radiant energy in said envelope, a gas or vapor in said envelope which dissociates in the presence of hot tungsten, and a gas or vapor in said envelope which converts the heat of recombination of the dissociated gas or Vapor into visible light.

6. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source of radiant energy in said envelope, hydrogen in said envelope which dissociates in the presence of hot tungsten, and a gas or vapor in said envelope which converts the heat of recombination of the dissociated hydrogen into visible light.

7. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source of radiant energy in said envelope, a gas or vapor in said envelope which dissociates in the presence of hot tungsten, and phosphorous vapor in said envelope which converts the heat of recombination of the dissociated gas or vapor into visible light.

8. A light source comprising an evacuated light transmitting envelope, an incandescible tungsten source of radiant energy in said envelope, hydrogen in said envelope which dissociates in the presence of hot tungsten, and phosphorous vapor in said envelope which converts the heat of recombination of the dissociated hydrogen into visible light.

References Cited in the file of this patent UNITED STATES PATENTS 1,186,993 Keyes June 13, 1916 1,249,978 MacKay Dec. 11, 1917 1,463,178 Shackelford July 3l, 1923 1,572,607 Jenkins Feb. 9, 1926 1,572,670 Myers Feb. 9, 1926 2,114,175 Cartun Apr. 12, 1938 2,221,644 Lucian Nov. 12, 1940 2,748,303 Thorington May 29, 1956 2,759,119 Thorington Aug. 14, 1956 

1. A LIGHT SOURCE COMPRISING AN EVACUATED LIGHT TRANSMITTING ENVELOPE, AN INCANDESCIBLE TUNGSTEN SOURCE OF RADIANT ENERGY IS SAID ENEVLOPE, A GAS OR VAPOR IN SAID ENVELOPE AT OR BELOW A PRESSURE OF 200 MILLIMETERS WHICH DISSOCIATES IN THE PRESENCE OF HOT TUNGSTEN, AND ANOTHER 